Semiconductor devices such as semiconductor integrated circuits and the like are generally produced by using several types of semiconductor-manufacturing devices to repeatedly carry out etching, CVD film formation, or the like, on semiconductor wafers or the like. In such cases a mass flow controlling device such as a mass flow controller is used because of the need to precisely control the supply of trace amounts of processing gas (See Japanese Unexamined Patent Applications (Kokai) 6-119059, 7-078296, 7-134052, 7-281760, 7-306084, 11-223538, and 2004-20306, U.S. Pat. No. 6,450,200, and Japanese Unexamined Patent Applications (Kokai) 8-185229 and 11-154022).
The structure of common mass flow controllers is illustrated in FIGS. 17 and 18. FIG. 17 schematically illustrates the structure of an example of a conventional mass flow controller inserted into a gas tube, and FIG. 18 is a circuit diagram illustrating the flow detection means in a mass flow controller.
As illustrated, the mass flow controller 2 is inserted into a flow channel, such as a gas tube 4, through which a fluid such as a liquid or gas flows, so as to control the mass flow. A vacuum is created, for example, in the interior of the semiconductor manufacturing device connected to one end of the gas tube 4. The mass flow controller 2 has a channel 6 formed by means of stainless steel, for example, both ends of which are connected to the gas tube 4. The mass flow controller 4 includes mass flow detection means 8 located in the upstream stage of the channel 6, and a flow control valve mechanism 10 located in the downstream stage.
The mass flow detection means 8 has a bypass group 12 comprising a bundle of a plurality of bypass tubes located upstream in the direction in which the gas fluid flows in the channel 6. A sensor tube 14 is connected to both ends of the bypass group 12 to bypass the group, allowing a smaller amount of gas fluid compared to the bypass group 12 to flow at a constant rate therein. That is, a constant proportion of gas relative to the total gas flow always flows into the sensor tube 14. A pair of control resistor wires R1 and R4 connected in series are wound around the sensor tube 14, and flow signals S1 indicating the mass flow level are output by a sensor circuit 16 connected thereto.
The flow signal S1 is input to a control means 18 forming using a micro-computer, for example. The mass flow of the gas currently flowing is determined based on the flow signal S1. The flow control valve mechanism is controlled so that the determined mass flow is consistent with the mass flow represented by an input flow set signal S0. The flow control valve mechanism 10 has a flow control valve 20 located on the downstream side of the channel 6. The flow control valve 20 has a diaphragm 22 made of bendable metal plate, for example, as a valve for directly controlling the mass flow of the gas fluid.
The diaphragm 22 is moved toward the valve opening 24 by being appropriately bent and reshaped, to allow the aperture or the opening degree of the valve opening 24 to be controlled as desired. The upper surface of the diaphragm 22 is connected to the bottom end of an actuator 26 formed using a laminated piezoelectric element (piezo element), thereby allowing the aperture to be adjusted in the manner described above. The actuator 26 is operated by means of the valve drive voltage S2 output by the valve drive circuit 28 upon receiving a drive signal from the control means 18. A sonic nozzle 29 is provided on the outlet side of the valve opening 24, and the gas flow inlet side pressure is set so as to be proportional to the mass flow flowing through the flow control valve 20. An electromagnetic actuator may sometimes be used instead of a laminated piezoelectric element as the actuator 26.
FIG. 18 illustrates the relationship between the sensor circuit 16 and the resistor wires R1 and R4. That is, the serially connected circuits of two reference resistors R2 and R3 are connected in parallel to the serial connection of the resistor wires R1 and R4, forming what is referred to as a bridge circuit. A constant current source 30 for the flow of constant current is connected to the bridge circuit. The connecting point of the resistor wires R1 and R4 and the connecting point of the reference resistors R2 and R3 are connected to the input side, for providing a differential circuit 32. The difference in potential between the two connecting points is determined, and the difference in potential is output in the form of a flow signal S1.
The resistor wires R1 and R4 consist of materials in which the resistance levels vary in response to temperature. The resistor wire R1 is wound around the upstream side in the direction in which the gas flows, and the resistor wire R4 is wound around the downstream side.
When the gas fluid does not flow to the sensor tube 14 in the mass flow controller 2 constructed in the manner described above, since the temperature of the two resistor wires R1 and R4 are the same, the bridge circuit is in equilibrium, and the difference in potential, which is the detected level of the differential circuit 32, is zero, for example.
When the gas fluid flows at a mass flow Q to the sensor tube 14, the gas fluid flows to the position where the resistor wire R4 on the downstream side is wound while warmed by the heat of the resistor wire R1 located on the upstream side. As a result, the heat travels, causing differences in temperature between the resistor wires R1 and R4, that is, differences in the resistance level between the two resistor wires R1 and R4. The difference in potential produced by the differences in the resistance level is virtually proportional to the mass flow of the gas. A certain level of gain in the flow signal S1 thus allows the flow rate of the gas flowing at that time to be determined. The aperture of the flow control valve 20 is controlled by a PID control method, for example, so that the gas mass flow that is detected is consistent with the mass flow represented by the flow set signal S0 (actually, the potential value).
In this type of mass flow controller 2, however, the actual flow in the flow control valve 20 (referred to below as “actual flow”) must be precisely consistent with the mass flow represented by the flow set signal (referred to below as “flow”), but when the feed gas pressure changes, or when the device itself changes over time, etc., the application of valve drive voltage equal to the initial level delivered to the device sometimes results in slight differences in the actual flow of the gas.
In view of the foregoing, the present invention was devised in order to effectively address the above problems. An object of the invention is to provide a flow control device and adjustment method in which flow deviation is measured by the device itself.
The present invention relates to Japanese Patent Applications 2004-182362 and 2005-153314, the details of which are hereby incorporated by reference.